Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Further, engines have been proposed using more than one type of fuel injection. For example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. are one example. Specifically, the Heywood et al. papers describe directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. The ethanol provides increased octane and increased charge cooling due to its higher heat of vaporization compared with gasoline, thereby reducing knock limits on boosting and/or compression ratio. Further, water may be mixed with ethanol and/or used as an alternative to ethanol. The above approaches purport to improve engine fuel economy and increase utilization of renewable fuels.
However, the inventors herein have recognized several issues with such an approach. Specifically, requiring a user to always provide separate fuels (e.g., gasoline and ethanol) can be burdensome to the operator. To simplify use of an engine with more than one type of fuel injection, the inventors herein have recognized that such an approach may be more easily implemented by the use of an apparatus comprising a fuel separator disposed between the fuel tank and engine, the separator comprising a first passageway and a second passageway separated at least partially by a selective barrier that selectively transports one of an alcohol fuel and a hydrocarbon fuel at a higher rate than the other of the alcohol fuel and the hydrocarbon fuel, and an exhaust gas recirculation conduit or other extraction fluid source in fluid communication with the second passage fuel separator; and by the use of a method comprising providing fuel from the fuel tank to the first passageway of the fuel separator, and flowing an extraction fluid through the second passageway of the fuel separator. This approach takes advantage of already available gas/alcohol mixtures, and therefore may allow advantages of multiple injection and/or multiple fuel strategies to be employed without inconveniencing a user. Furthermore, the use of the extraction fluid may help to drive the transport of the extracted fuel components across the selective barrier, thereby increasing transport rates. Additionally, in embodiments where recirculated exhaust gas is used as an extraction fluid, the extraction fluid may also be used to heat the separator, which may further help increase transport rates. These and other advantages are discussed in more detail below.